Most electronic devices are assembled by soldering their constituent components together. In the soldering process, a metal alloy is melted and used to join two adjacent metal surfaces together. The metallic surfaces which are to be joined are heated. The soldering material is then brought into contact with the heated surfaces. The alloy is chosen such that its melting point is fairly low. The solder is most often lead or tin based. The heated metallic surfaces causes the solder to become liquid and flow around the parts to be joined. When the solder cools and solidifies, a solid joint is thereby formed between the two elements. Because the joining medium is metallic, the soldering process result in a good electrical contact between the two elements which are joined.
In order to facilitate the soldering process, a material known as flux may be brought into contact with the solder in order to induce the melting of the solder. Flux is a rosin based material. It is used to clean the metallic surfaces and free them of oxides. This results in better thermal contact between the elements to be joined and enhances the melting of the solder.
In the past, solder was applied to the elements to be joined with a hypodermic needle means. During this process, a tremendous amount of excess, unused, flux was also deposited. The addition of flux to the soldering process has its disadvantages in that it can deteriorate the quality of the electrical contact between the elements which are joined. The excess flux must be removed via a cleaning process. This can involve the use of unwanted chemicals, such as freon.
For this reason, it is desirable that the minimum amount of flux necessary to be used during the soldering process, and that the flux be accurately deposited at the desired location. Devices are known in the prior art which use ultrasonic methods to provide a fine spray of flux. This fine spray can be applied to a given area which is to be soldered.
The ultrasonic devices typically consist of a relatively long, thin nozzle which is vibrated at a high frequency. Liquid flux enters the ultrasonic device and, as it passes through the nozzle, is broken into small droplets by the vibration of the nozzle. The small droplets exit the nozzle in the form of an atomized vapor spray. The ultrasonic devices reduce the amount of flux which must be used because the smaller elements of the flux can easily attach to the items which are to be soldered. These devices have the drawback, however, that they disperse the flux over a relatively large area and cannot be precisely aimed. As noted above, this may result in a poor electrical contact in the items which are to be joined, which could result in a deterioration of the operation of the overall assembly. Also, the need to clean the device is, for most cases, obviated.